Ice-free summers--a phenomenon that hasn't occurred in the Arctic in a million years--could become a reality in a century because of warming trends, researchers said.

Looking at data on the rate of ice melt in the Arctic, researchers from the University of Arizona and other universities concluded that the rate is accelerating and that no foreseeable natural forces will counteract that acceleration. As a result, ice-free summers loom.

The situation will have worldwide ecological impact, the researchers said. The progressive melt will cause sea levels worldwide to rise, flooding coastal areas, where a substantial portion of the world's population lives. Huge sections of Bangladesh, for example, consist of river delta at sea level. The melt could also thaw permafrost, which could lead to an increase of greenhouse gases in the atmosphere.

The increasing rate of ice melt is already having some impact on people and animals in the Arctic. Other researchers have speculated that the progressing ice melt around Siberia may lead to a summer Northeast passage connecting Japan to Europe in a decade or so.

Some researchers have also speculated that sea levels may rise nearly a foot in 100 years.

The climate of the Arctic region has veered from deep ice ages where glaciers covered huge swaths of North America and Europe to somewhat warmer periods. By studying ice cores and marine sediment, scientists have put together a picture of the natural climate envelope for the region for the past million years.

Arctic climate is largely determined by the interplay of three different feedback loops: the interaction between sea and land ice; ocean circulation in the North Atlantic; and precipitation and evaporation. Shifts in the balance of these factors lead inexorably to larger changes.

For example, the white surface of sea ice reflects radiation from the sun. However, as sea ice melts, more solar radiation is absorbed by the dark ocean, which heats up and results in yet more sea ice melting.

While some of these factors could cause the rate of the melt to slow, none appear strong enough to reverse the current situation, the researchers said.

"I think probably the biggest surprise of the meeting was that no one could envision any interaction between the components that would act naturally to stop the trajectory to the new system," said Jonathan Overpeck, a geoscientist at the University of Arizona and the lead author on the paper.

The report was published in the Aug. 23 edition of Eos, the weekly newspaper of the American Geophysical Union.